Compound, hole transport material, and photoelectric conversion element using same

Abstract

The problem to be solved by the present invention is to provide: a compound, which is useful as a hole transport material for a photoelectric conversion element that is capable of efficiently extracting an electric current; and a photoelectric conversion element and a solar cell, which use said compound in a hole transport layer, and have good photoelectric conversion characteristics and high heat resistance.　The present invention is a compound, which is represented by general formula (1). In the formula: R1 to R4 represent 6- to 36-carbon aromatic hydrocarbon groups, etc. having a substituent; R5 and R6 represent hydrogen atoms, 1- to 20-carbon linear or branched alkyl groups, etc. which may have a substituent; and X1 and X2 represent divalent groups, etc. of a 6- to 36-carbon aromatic hydrocarbon group, which may have a substituent.

Description

Compound, hole transport material, and photoelectric conversion element using the same

[0001] The present invention relates to a compound, a hole transport material, and a photoelectric conversion element using the same.

[0002] In recent years, solar power generation has attracted attention as a clean energy source, and the development of solar cells has been actively pursued. Among these, the development of solar cells using perovskite materials in the photoelectric conversion layer (hereinafter referred to as perovskite solar cells) has attracted attention as a next-generation solar cell that can be manufactured at low cost using a solution process (for example, Patent Document 1, Non-Patent Documents 1 and 2).

[0003] Perovskite solar cells often use hole transport materials in their devices. The purposes of their use include (1) enhancing the ability to selectively transport holes and thereby improving photoelectric conversion efficiency, and (2) protecting the perovskite material, which is susceptible to moisture and oxygen, by bonding with the perovskite photoelectric conversion layer (see, for example, Non-Patent Document 3). Spiro-OMeTAD, a spirobifluorene-based organic compound, is often used as a standard hole transport material, but there have been few reports of hole transport materials that contribute more significantly to photoelectric conversion properties than this material. Furthermore, since photoelectric conversion devices are expected to be used outdoors under sunlight irradiation, high heat resistance is required.

[0004] US10937972 B2

[0005] Journal of the American Chemical Society, 2009, Vol. 131, pp. 6050-6051 Science, 2012, Vol. 388, pp. 643-647 Chem. Sci., 2019, 10, pp. 6748-6769

[0006] The problem to be solved by the present invention is to provide a compound useful as a hole transport material for a photoelectric conversion element that can extract current efficiently, and to provide a photoelectric conversion element and a solar cell that use the compound in a hole transport layer and have good photoelectric conversion characteristics and high heat resistance.

[0007] In order to solve the above problems, the inventors conducted extensive research into improving photoelectric conversion properties and, as a result, designed and developed a compound having a dithienoquinoxaline skeleton structure and found that by using the compound as a hole transport layer in a photoelectric conversion element, a photoelectric conversion element and a perovskite solar cell exhibiting high photoelectric conversion efficiency can be obtained.

[0008] 1. A compound represented by the following general formula (1):

[0009]

[0010] In the formula, R １ ~R ４ each independently represents a hydrogen atom, an optionally substituted linear or branched alkyl group of 1 to 20 carbon atoms, an optionally substituted linear or branched alkenyl group of 2 to 20 carbon atoms, an optionally substituted cycloalkyl group of 3 to 10 carbon atoms, an optionally substituted aromatic hydrocarbon group of 6 to 36 carbon atoms, or an optionally substituted heterocyclic group of 5 to 36 ring atoms, R １ and R ２ , and R ３ and R ４ may be bonded to each other to form a ring. ５ and R ６X each independently represent a hydrogen atom, a halogen atom, a cyano group, a carboxyl group, a trimethylsilyl group, a linear or branched alkyl group of 1 to 20 carbon atoms which may have a substituent, a linear or branched alkenyl group of 2 to 20 carbon atoms which may have a substituent, a cycloalkyl group of 3 to 10 carbon atoms which may have a substituent, a linear or branched alkoxy group of 1 to 20 carbon atoms which may have a substituent, a cycloalkoxy group of 3 to 10 carbon atoms which may have a substituent, a linear or branched acyl group of 1 to 20 carbon atoms which may have a substituent, a thio group of 0 to 20 carbon atoms which may have a substituent, an amino group of 0 to 30 carbon atoms which may have a substituent, an aromatic hydrocarbon group of 6 to 36 carbon atoms which may have a substituent, or a heterocyclic group of 5 to 36 ring atoms which may have a substituent. １ and X ２ each independently represents a single bond, a divalent aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent, a divalent heterocyclic group having 5 to 36 ring atoms which may have a substituent, or a divalent group containing the aromatic hydrocarbon group and the heterocyclic group; X １ and R １ , X １ and R ２ , X ２ and R ３ , and X ２ and R ４ may be bonded to each other to form a ring.

[0011] 2. In the general formula (1), R １ ~R ４ are each independently a substituted aromatic hydrocarbon group having 6 to 36 carbon atoms.

[0012] 3. In the general formula (1), X １ and X ２ are each independently a divalent group of an unsubstituted aromatic hydrocarbon group having 6 to 36 carbon atoms.

[0013] 4. A hole transport material comprising the compound.

[0014] 5. A photoelectric conversion element using the hole transport material.

[0015] 6. A solar cell using the photoelectric conversion element.

[0016] By using the compound according to the present invention and a hole transport layer using the compound, it is possible to obtain a photoelectric conversion element and a perovskite solar cell having good photoelectric conversion efficiency and high heat resistance.

[0017] 1A and 1B are schematic cross-sectional views illustrating the configurations of photoelectric conversion elements according to examples of the present invention and comparative examples.

[0018] DETAILED DESCRIPTION OF THE INVENTION The compound of the present invention is suitably used as a hole transport material in photoelectric conversion elements and perovskite solar cells.

[0019] The compounds represented by the general formula (1) will be specifically explained below, but the present invention is not limited thereto.

[0020] In general formula (1), R １ ~R ４ each independently represents a hydrogen atom, a linear or branched alkyl group of 1 to 20 carbon atoms which may have a substituent, a linear or branched alkenyl group of 2 to 20 carbon atoms which may have a substituent, a cycloalkyl group of 3 to 10 carbon atoms which may have a substituent, an aromatic hydrocarbon group of 6 to 36 carbon atoms which may have a substituent, or a heterocyclic group of 5 to 36 ring atoms which may have a substituent.

[0021] In general formula (1), R １ ~R ４ Specific examples of the "straight-chain or branched alkyl group having 1 to 20 carbon atoms" in the "straight-chain or branched alkyl group having 1 to 20 carbon atoms which may have a substituent" represented by the formula (1) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, a 2-ethylhexyl group, a heptyl group, an octyl group, an isooctyl group, a nonyl group, and a decyl group.

[0022] In general formula (1), R １ ~R４ Specific examples of the "straight-chain or branched alkenyl group having 2 to 20 carbon atoms" in the "straight-chain or branched alkenyl group having 2 to 20 carbon atoms which may have a substituent" represented by the formula (1) include ethenyl group (vinyl group), 1-propenyl group, 2-propenyl group (allyl group), 1-methylethenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 1-hexenyl group, 2-methyl-1-propenyl group, 2-methyl-2-propenyl group, 1-ethylethenyl group, and straight-chain or branched alkenyl groups having 2 to 20 carbon atoms in which a plurality of these alkenyl groups are bonded.

[0023] In general formula (1), R １ ~R ４ Specific examples of the "cycloalkyl group having 3 to 10 carbon atoms" in the "cycloalkyl group having 3 to 10 carbon atoms which may have a substituent" represented by the formula (1) include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecyl group, a cyclododecyl group, a 4-methylcyclohexyl group, and a 4-ethylcyclohexyl group.

[0024] In general formula (1), R １ ~R ４ Specific examples of the "aromatic hydrocarbon group having 6 to 36 carbon atoms" in the "aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent" represented by the formula (1) include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, an anthracenyl group (anthryl group), a phenanthryl group, a fluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, a triphenylenyl group, etc. In the present invention, the aromatic hydrocarbon group is considered to include a "condensed polycyclic aromatic group."

[0025] In general formula (1), R １ ~R ４Specific examples of the "heterocyclic group having 5 to 36 ring atoms" in the "heterocyclic group having 5 to 36 ring atoms which may have a substituent" represented by the formula (I) include a pyridyl group, a pyrimidinyl group, a triazinyl group, a thienyl group, a furyl group (furanyl group), a pyrrolyl group, an imidazolyl group, a pyrazolyl group, a triazolyl group, a quinolyl group, an isoquinolyl group, a naphthyldinyl group, an acridinyl group, a phenanthrolinyl group, a benzofuranyl group, a benzothienyl group, an oxazolyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a thiazolyl group, a benzothiazolyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, and a carbonyl group.

[0026] In general formula (1), R １ ~R 4 Specific examples of the "substituent" in the "optionally substituted linear or branched alkyl group having 1 to 20 carbon atoms," "optionally substituted linear or branched alkenyl group having 2 to 20 carbon atoms," "optionally substituted cycloalkyl group having 3 to 10 carbon atoms," "optionally substituted aromatic hydrocarbon group having 6 to 36 carbon atoms," or "optionally substituted heterocyclic group having 5 to 36 ring atoms" represented by the above formula include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom; cyano group; hydroxyl group; nitro group; nitroso group; carboxyl group; phosphate group; thioxo group (>C=S); trimethylsilyl group; sulfonic acid group; sulfonate group (-SO ３X: X represents an alkali metal cation other than hydrogen); carboxylic acid ester groups such as a methyl ester group and an ethyl ester group; linear or branched alkyl groups having 1 to 18 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, a 2-ethylhexyl group, a heptyl group, an octyl group, an isooctyl group, a nonyl group, or a decyl group; linear or branched alkenyl groups having 2 to 18 carbon atoms such as an ethenyl group (vinyl group), a 1-propenyl group, a 2-propenyl group (allyl group), a 1-butenyl group, a 2-butenyl group, a 1-pentenyl group, a 1-hexenyl group, a 2-methyl-1-propenyl group, a 2-methyl-2-propenyl group, or a 1-ethylethenyl group; a methoxy group, an ethoxy group, a propoxy group, a t -Alkoxy groups having 1 to 18 carbon atoms, such as butoxy, pentyloxy, and hexyloxy; aromatic hydrocarbon groups having 6 to 30 carbon atoms, such as phenyl, naphthyl, anthryl, phenanthryl, and pyrenyl; pyridyl, pyrimidinyl, triazinyl, thienyl, furyl (furanyl), pyrrolyl, imidazolyl, pyrazolyl, triazolyl, quinolyl, and isoquinolyl groups. heterocyclic groups having 5 to 30 ring atoms such as a naphthyldinyl group, an acridinyl group, a phenanthrolinyl group, a benzofuranyl group, a benzothienyl group, an oxazolyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a thiazolyl group, a benzothiazolyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, or a carbonylyl group; unsubstituted amino groups (-NH ２Examples of such substituents include amino groups having 0 to 18 carbon atoms, such as monosubstituted amino groups such as methylamino, ethylamino, acetylamino, and phenylamino, or disubstituted amino groups such as dimethylamino, diethylamino, diphenylamino, and acetylphenylamino; unsubstituted thio groups (thiol groups: —SH), and thio groups having 0 to 18 carbon atoms, such as methylthio, ethylthio, propylthio, phenylthio, and biphenylthio. These "substituents" may be present in only one or more groups, and when present in multiple groups, they may be the same or different. Adjacent substituents may be bonded to each other via a single bond, an oxygen atom, a sulfur atom, a selenium atom, or a nitrogen atom to form a ring. Furthermore, these "substituents" may further have the substituents exemplified above.

[0027] In the present invention, R in general formula (1) １ ~R ４ is preferably a cycloalkyl group having 3 to 10 carbon atoms which may have a substituent, an aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent, or a heterocyclic group having 5 to 36 ring atoms which may have a substituent, and more preferably an unsubstituted cycloalkyl group having 3 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 36 carbon atoms which has a substituent. １ ~R ４ is preferably a 4-alkoxyphenyl group in which the alkoxy group has 1 to 5 carbon atoms. １ ~R ４ is a 4-[bis(4-alkoxyphenyl)amino]phenyl group in which the alkoxy group has 1 to 5 carbon atoms, and R １ and R ２ , and R ３ and R ４ are preferably bonded to each other via a single bond to form a ring. １ and R ３ is a 4-(2,2-diphenylethenyl)phenyl group, and R ２ and R ４ is a cyclopentyl group, and R ２ and R４ But, X １ and X ２ and are preferably bonded to each other via a single bond.

[0028] In general formula (1), R １ and R ２ , and R ３ and R ４ may be bonded to each other via a single bond, or a bond via an oxygen atom, a sulfur atom, a selenium atom, or a nitrogen atom to form a ring. １ and R ２ , and R ３ and R ４ When these form a ring, they are preferably bonded to each other via a single bond, or a bond via an oxygen atom or a sulfur atom.

[0029] In general formula (1), R ５ and R ６ each independently represent a hydrogen atom, a halogen atom, a cyano group, a carboxyl group, a trimethylsilyl group, a linear or branched alkyl group of 1 to 20 carbon atoms which may have a substituent, a linear or branched alkenyl group of 2 to 20 carbon atoms which may have a substituent, a cycloalkyl group of 3 to 10 carbon atoms which may have a substituent, a linear or branched alkoxy group of 1 to 20 carbon atoms which may have a substituent, a cycloalkoxy group of 3 to 10 carbon atoms which may have a substituent, a linear or branched acyl group of 1 to 20 carbon atoms which may have a substituent, a thio group of 0 to 20 carbon atoms which may have a substituent, an amino group of 0 to 30 carbon atoms which may have a substituent, an aromatic hydrocarbon group of 6 to 36 carbon atoms which may have a substituent, or a heterocyclic group of 5 to 36 ring atoms which may have a substituent.

[0030] In general formula (1), R ５ and R ６ Examples of the "halogen atom" represented by the formula include fluorine, chlorine, bromine and iodine.

[0031] In general formula (1), R ５ and R ６In the "straight-chain or branched alkyl group having 1 to 20 carbon atoms which may have a substituent" represented by the formula (1), the "straight-chain or branched alkyl group having 1 to 20 carbon atoms" is, for example, １ ~R ４ Examples of the alkyl group include the same as the "straight-chain or branched alkyl group having 1 to 20 carbon atoms which may have a substituent" represented by the following formula:

[0032] In general formula (1), R ５ and R ６ The "straight-chain or branched alkenyl group having 2 to 20 carbon atoms" in the "straight-chain or branched alkenyl group having 2 to 20 carbon atoms which may have a substituent" represented by the general formula (1) includes R １ ~R ４ Examples of the alkyl group include the same as the "straight-chain or branched alkenyl group having 2 to 20 carbon atoms which may have a substituent" represented by the following formula:

[0033] In general formula (1), R ５ and R ６ The "cycloalkyl group having 3 to 10 carbon atoms" in the "cycloalkyl group having 3 to 10 carbon atoms which may have a substituent" represented by the general formula (1) is, for example, R １ ~R ４ Examples of the cycloalkyl group include the same as the "cycloalkyl group having 3 to 10 carbon atoms which may have a substituent" represented by the following formula:

[0034] In general formula (1), R ５ and R ６Specific examples of the "alkoxy group having 1 to 20 carbon atoms" in the "alkoxy group having 1 to 20 carbon atoms which may have a substituent" represented by the formula (1) include a methoxy group, an ethoxy group, a propoxy group, an n-butoxy group, an n-pentyloxy group, an n-hexyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group, an isopropoxy group, an isobutoxy group, an s-butoxy group, a t-butoxy group, an isooctyloxy group, a t-octyloxy group, a phenoxy group, a tolyloxy group, a biphenylyloxy group, a terphenylyloxy group, a naphthyloxy group, an anthryloxy group, a phenanthryloxy group, a fluorenyloxy group, and an indenyloxy group.

[0035] In general formula (1), R ５ and R ６ Specific examples of the "cycloalkoxy group having 3 to 10 carbon atoms" in the "cycloalkoxy group having 3 to 10 carbon atoms which may have a substituent" represented by the formula (1) include a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, a cyclohexyloxy group, and a 4-methylcyclohexyloxy group.

[0036] In general formula (1), R ５ and R ６ Specific examples of the "acyl group having 1 to 20 carbon atoms" in the "acyl group having 1 to 20 carbon atoms which may have a substituent" represented by the formula (1) include an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a valeryl group, an isovaleryl group, a benzoylacetyl group, a benzoyl group, etc., and when it contains an alkyl chain, it includes one in which hydrogen atoms are completely substituted with fluorine atoms (perfluorinated). It may also be one bonded to an amino group (-CO-N<).

[0037] In general formula (1), R ５ and R ６ Specific examples of the "thio group having 0 to 20 carbon atoms" in the "thio group having 0 to 20 carbon atoms which may have a substituent" represented by the formula (1) include a methylthio group, an ethylthio group, a propylthio group, a phenylthio group, and a biphenylthio group.

[0038] In general formula (1), R ５ and R ６ In the general formula (1), specific examples of the "amino group having 1 to 30 carbon atoms" in the "amino group having 0 to 30 carbon atoms which may have a substituent" represented by the formula (1) include monosubstituted amino groups such as an ethylamino group, an acetylamino group, and a phenylamino group, and disubstituted amino groups such as a diethylamino group, a diphenylamino group, and an acetylphenylamino group.

[0039] In general formula (1), R ５ and R ６ The "aromatic hydrocarbon group having 6 to 36 carbon atoms" in the "aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent" represented by the general formula (1) is, for example, R １ ~R ４ Among the "aromatic hydrocarbon groups having 6 to 36 carbon atoms which may have a substituent" represented by the following formula, the same as the "aromatic hydrocarbon groups having 6 to 36 carbon atoms" can be mentioned.

[0040] In general formula (1), R ５ and R ６ The "heterocyclic group having 5 to 36 ring atoms" in the "heterocyclic group having 5 to 36 ring atoms which may have a substituent" represented by the formula (1) is, for example, a heterocyclic group having 5 to 36 ring atoms which may have a substituent, represented by the formula (1), １ ~R ４ Among the "heterocyclic group having 5 to 36 ring atoms which may have a substituent" represented by the following formula, the same as the "heterocyclic group having 5 to 36 ring atoms" can be mentioned.

[0041] In general formula (1), R ５ and R ６Examples of the "substituent" in the "linear or branched alkyl group of 1 to 20 carbon atoms which may have a substituent", "linear or branched alkenyl group of 2 to 20 carbon atoms which may have a substituent", "cycloalkyl group of 3 to 10 carbon atoms which may have a substituent", "linear or branched alkoxy group of 1 to 20 carbon atoms which may have a substituent", "cycloalkoxy group of 3 to 10 carbon atoms which may have a substituent", "linear or branched acyl group of 1 to 20 carbon atoms which may have a substituent", "thio group of 1 to 20 carbon atoms which may have a substituent", "amino group of 0 to 30 carbon atoms which may have a substituent", "aromatic hydrocarbon group of 6 to 36 carbon atoms which may have a substituent", or "heterocyclic group of 5 to 36 ring atoms which may have a substituent" represented by the general formula (1) include R １ ~R ４ Examples of the "substituent" include the same as those in the "straight-chain or branched alkyl group having 1 to 20 carbon atoms which may have a substituent" represented by the following formula:

[0042] In the present invention, R in general formula (1) ５ and R ６ is preferably a hydrogen atom, a cyano group, a linear or branched alkyl group of 1 to 20 carbon atoms which may have a substituent, a linear or branched alkoxy group of 1 to 20 carbon atoms which may have a substituent, a thio group of 1 to 20 carbon atoms which may have a substituent, or an amino group of 0 to 30 carbon atoms which may have a substituent, and more preferably a hydrogen atom or a linear or branched alkyl group of 1 to 5 carbon atoms.

[0043] In general formula (1), X １ and X ２ each independently represents a single bond, a divalent aromatic hydrocarbon group having 6 to 36 carbon atoms and having a substituent, a divalent heterocyclic group having 5 to 36 ring atoms and having a substituent, or a divalent group containing the aromatic hydrocarbon group and the heterocyclic group.

[0044] In general formula (1), X １ and X ２In the "divalent group of an aromatic hydrocarbon group having 6 to 36 carbon atoms (arylene group) having a substituent" represented by the formula (1), the aromatic ring constituting the "arylene group having 6 to 36 carbon atoms" may be a monocycle, a fused ring in which two or more rings are fused, or a linked ring in which two or more rings are linked by a single bond. Examples of the "divalent group of an aromatic hydrocarbon group having 6 to 36 carbon atoms (arylene group) which may have a substituent" include those represented by the formula (1), １ ~R ４ Among the "aromatic hydrocarbon groups having 6 to 36 carbon atoms which may have a substituent" represented by the following formula (1), examples include the same as the "aromatic hydrocarbon group having 6 to 36 carbon atoms", and examples thereof include a divalent group obtained by removing one hydrogen atom from a monovalent aromatic hydrocarbon group (aryl group) and a divalent group obtained by removing one hydrogen atom from a substituted aryl group in which at least one hydrogen atom of the aryl group has been substituted with a substituent (the former divalent group is preferred).

[0045] In general formula (1), X １ and X ２ The heterocycle constituting the "divalent heterocyclic group having 5 to 36 ring atoms" in the "divalent heterocyclic group having 5 to 36 ring atoms which may have a substituent" represented by the formula (1) may be a monocycle or a condensed ring in which two or more rings are condensed. The heterocycle may be an aromatic heterocycle or an aliphatic heterocycle. Examples of heteroatoms constituting the heterocycle include a nitrogen atom, an oxygen atom, and a sulfur atom. Specific examples of the "divalent heterocyclic group having 5 to 36 ring atoms" include those represented by the formula (1) １ ~R ４ Among the "heterocyclic group having 5 to 36 ring atoms which may have a substituent" represented by the following formula (I), examples thereof include the same as the "heterocyclic group having 5 to 36 ring atoms", and examples thereof include a divalent group obtained by removing one hydrogen atom from a monovalent heterocyclic group, and a divalent group obtained by removing one hydrogen atom from a substituted heterocyclic group in which at least one hydrogen atom of a monovalent heterocyclic group has been substituted with a substituent (the former divalent group is preferred).

[0046] In general formula (1), X １ and X ２may be a divalent group containing the "optionally substituted aromatic hydrocarbon group having 6 to 36 carbon atoms" and the "optionally substituted heterocyclic group having 5 to 36 ring atoms" (a divalent group containing the aromatic hydrocarbon group and the heterocyclic group).

[0047] X in general formula (1) １ and X ２ is not a single bond, X １ and R １ , X １ and R ２ , X ２ and R ３ , and X ２ and R ４ may be bonded to each other by a single bond or a bond via an oxygen atom, a sulfur atom, a selenium atom, or a nitrogen atom to form a ring.

[0048] In general formula (1), X １ and X ２ are each independently preferably a divalent unsubstituted aromatic hydrocarbon group having 6 to 36 carbon atoms, and more preferably a 1,4-phenylene group.

[0049] Specific examples of the compound represented by the general formula (1) of the present invention are shown below, but the present invention is not limited to these. Furthermore, the following exemplary compounds are shown with some hydrogen atoms, carbon atoms, etc. omitted, and are examples of possible isomers, but all other isomers are included. Furthermore, each may be a mixture of two or more isomers.

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] The compound of the present invention represented by the general formula (1) can be synthesized by known methods.

[0076] A dibromodithienoquinoxaline derivative represented by the following formula (5) can be synthesized by carrying out a dehydration condensation reaction using a compound represented by the following formula (3) and a diamine compound represented by the following formula (4), and the derivative can be further synthesized by carrying out a Suzuki-Miyaura cross-coupling reaction with a boronic acid compound represented by the following general formulas (6) and (7), or a boronic acid ester compound represented by the following general formulas (8) and (9).

[0077]

[0078] X in the formula １ , X ２ and R １ ~R ４ has the same meaning as in the general formula (1).

[0079] X in the formula １ , X ２ and R １ ~R ４ has the same meaning as in the general formula (1).

[0080] The compound represented by the general formula (1) of the present invention can be purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization or crystallization using a solvent, etc. In the present invention, it is effective to use a compound with increased purity by using these methods in combination. Furthermore, these compounds can be identified by nuclear magnetic resonance analysis (NMR).

[0081] Preferred embodiments of the photoelectric conversion element of the present invention will be described below.

[0082] As shown in FIG. 1 , the photoelectric conversion element of the present invention preferably comprises a conductive support 1, an electron transport layer 2, a photoelectric conversion layer 3, a hole transport layer 4, and a counter electrode 5, but is not limited thereto. Furthermore, the photoelectric conversion element of the present invention is preferably used as a solar cell, and is more preferably a perovskite-type photoelectric conversion element, but is not limited thereto. In the present invention, the perovskite-type photoelectric conversion element preferably comprises a conductive support (electrode) 1, an electron transport layer 2, a photoelectric conversion layer (perovskite layer) 3, a hole transport layer 4, and a counter electrode 5, in this order. Alternatively, the photoelectric conversion element may be configured in the order of the conductive support, the hole transport layer, the photoelectric conversion layer (perovskite layer), the electron transport layer, and the counter electrode.

[0083] In the photoelectric conversion element of the present invention, the conductive support 1 shown in FIG. 1 must be translucent enough to transmit light that contributes to photoelectric conversion. In addition, the conductive support is preferably a conductive substrate because it is a member that has the function of extracting current from the photoelectric conversion layer. Specific examples of conductive materials include tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), tungsten-doped indium oxide (IWO), zinc aluminum oxide (AZO), fluorine-doped tin oxide (FTO), indium oxide (In ２ O ３ ), and conductive transparent oxide semiconductors such as indium-tin composite oxide, among which tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), and the like are preferably used.

[0084] In the photoelectric conversion element of the present invention, the electron transport layer 2 shown in Fig. 1 is a layer located between the conductive support 1 and the photoelectric conversion layer (perovskite layer) 3, and it is preferable, but not particularly limited to, that the electron transport layer 2 be formed on the conductive support 1. The electron transport layer is used to improve the efficiency of electron migration from the photoelectric conversion layer to the electrode and to block the migration of holes.

[0085] In the present invention, specific examples of the semiconductor that forms the electron transport layer include tin oxide (SnO, SnO ２ , SnO ３ etc.), titanium oxide (TiO ２ etc.), tungsten oxide (WO ２ , W.O. ３ , W ２ O ３ etc.), zinc oxide (ZnO), niobium oxide (Nb ２ O ５ etc.), tantalum oxide (Ta ２ O ５ etc.), yttrium oxide (Y ２ O ３ etc.), strontium titanate (SrTiO ３Examples of the semiconductor include metal oxides such as titanium sulfide, zinc sulfide, zirconium sulfide, copper sulfide, tin sulfide, indium sulfide, tungsten sulfide, cadmium sulfide, and silver sulfide; metal selenides such as titanium selenide, zirconium selenide, indium selenide, and tungsten selenide; and elemental semiconductors such as silicon and germanium, and it is preferable to use one or more of these semiconductors. In the present invention, it is preferable to use one or more of tin oxide, titanium oxide, and zinc oxide as the semiconductor.

[0086] In the present invention, a commercially available paste containing the semiconductor fine particles may be used to form the electron transport layer, or a paste (electron transport layer coating liquid) prepared by dispersing commercially available semiconductor fine powder in a solvent may be used. Specific examples of solvents used in preparing the paste include, but are not limited to, water; alcohol-based solvents such as methanol, ethanol, and isopropyl alcohol; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and hydrocarbon solvents such as n-hexane, cyclohexane, benzene, and toluene. Furthermore, these solvents may be used as a mixed solvent of two or more of them.

[0087] In the present invention, the semiconductor fine powder may be dispersed in a solvent after grinding the powder in a mortar or the like, or a dispersing machine such as a ball mill, a paint conditioner, a vertical bead mill, a horizontal bead mill, or an attritor may be used. When preparing a paste, it is preferable to add a surfactant or the like to prevent aggregation of the semiconductor fine particles, and it is also preferable to add a thickener such as polyethylene glycol to increase the viscosity.

[0088] In the present invention, the electron transport layer can be obtained using a known film-forming method depending on the material to be formed. The electron transport layer can be formed by any coating method using a coating liquid. Examples of the method include, but are not limited to, a wet coating method such as spin coating, inkjet printing, doctor blade printing, drop casting, squeegee printing, screen printing, reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire barber coating, pipe doctor printing, impregnation / coating, or curtain coating, followed by baking to remove solvents and additives, as well as sputtering, vapor deposition, electrodeposition, electrodeposition, and microwave irradiation. In the present invention, it is preferable to form a film by spin coating using the electron transport layer coating liquid prepared by the above method, but this is not limiting. The spin coating conditions can be appropriately set. The atmosphere in which the film is formed is not particularly limited, and the film may be formed in air.

[0089] From the viewpoint of further improving photoelectric conversion efficiency, when a dense layer is used, the thickness of the electron transport layer is usually preferably 5 nm to 100 nm, more preferably 10 nm to 50 nm. In the present invention, when a porous (mesoporous) metal oxide is used in addition to the dense layer, the thickness is usually preferably 20 nm to 200 nm, more preferably 50 nm to 150 nm.

[0090] In the photoelectric conversion element of the present invention, a photoelectric conversion layer (perovskite layer) 3 is preferably formed on the electron transport layer 2 shown in FIG.

[0091] When the photoelectric conversion element of the present invention is used as a perovskite-type photoelectric conversion element, the perovskite material of the photoelectric conversion layer is a compound represented by the general formula ABX ３ In this case, A, B, and X represent an organic cation or a monovalent metal cation, a metal cation, and a halide anion, respectively. Examples of A include K ＋ , Rb ＋ , Cs ＋, C.H. ３ NH ３ ＋ (hereinafter, MA: methylammonium), NH=CHNH ２ ＋ (hereinafter, FA: formamidinium), and CH ３ CH ２ NH ３ ＋ (hereinafter, EA: ethylammonium); examples of B include Pb and Sn; examples of X include I － , and Br － Furthermore, specific examples of perovskite materials include MAPbI ３ , FAPbI ３ , EAPbI ３ , CsPbI ３ , MASnI ３ , FASnI ３ , EASnI ３ , MAPbBr ３ , FAPbBr ３ , EAPbBr ３ , MASnBr ３ , FASnBr ３ , and EASnBr ３ Perovskite material represented by the composition: (FAMA)Pb(IBr) ３ , K(FAMA)Pb(IBr) ３ , Rb(FAMA)Pb(IBr) ３ , Cs(FAMA)Pb(IBr) ３ Examples of suitable perovskite materials include, but are not limited to, perovskite materials composed of mixed cations and / or mixed anions represented by the following composition: Two or more of these perovskite materials can be used. Furthermore, the perovskite material may contain a photoelectric conversion material other than the perovskite material.

[0092] The photoelectric conversion layer (perovskite layer) of the photoelectric conversion element of the present invention can be formed by any coating method using a coating liquid, and examples thereof include the same methods as those used to form the electron transport layer.

[0093] The perovskite precursor may be a commercially available material, and in the present invention, it is preferable to use a precursor consisting of lead halide, methylammonium halide, formamidine halide, or cesium halide in any composition, but the present invention is not limited to this.

[0094] From the viewpoint of precursor solubility, examples of solvents for the perovskite precursor solution of the present invention include, but are not limited to, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone. Two or more of these solvents may be mixed for use, and it is preferable to use a mixed solution of N,N-dimethylformamide and dimethyl sulfoxide. It is also preferable to use a dehydrated solvent with a water content of 10 ppm or less.

[0095] In the present invention, the atmosphere during deposition of the photoelectric conversion layer (perovskite layer) is preferably a dry atmosphere, more preferably a dry inert gas atmosphere such as a glove box, from the viewpoint of preventing moisture contamination and enabling the reproducible production of highly efficient perovskite solar cells. It is also preferable to dehydrate the layer using a molecular sieve or the like and use a solvent with a low moisture content.

[0096] In the present invention, the temperature at which the photoelectric conversion layer (perovskite layer) is heated using a hot plate or the like is preferably 50 to 200° C., more preferably 70 to 150° C., from the viewpoint of producing a perovskite material from the precursor. The heating time is preferably about 10 to 90 minutes, more preferably about 10 to 60 minutes.

[0097] The film thickness of the photoelectric conversion layer (perovskite layer) of the present invention is preferably 50 to 1000 nm, more preferably 300 to 700 nm, from the viewpoint of further suppressing performance degradation due to defects and peeling, and in order to ensure that the photoelectric conversion layer has sufficient light absorptivity and prevent the device resistance from becoming too high.

[0098] The photoelectric conversion layer (perovskite layer) of the present invention can increase the efficiency of interlayer charge transfer by covering surface defects and passivating the layer. Passivation can be achieved by any coating method using a coating liquid, including the same methods as those used to form the electron transport layer.

[0099] For passivation, it is preferable to use a compound having a quaternary ammonium salt structure, but this is not limitative and multiple compounds may be used in combination. Specific examples include phenylethylammonium bromide, n-hexylammonium bromide, and n-hexyltrimethylammonium bromide.

[0100] The passivation is preferably performed in a dry atmosphere. A method for removing the solvent from the coating solution is preferably a reduced pressure method. The coating thickness is not particularly limited as long as it has the effect of increasing the efficiency of charge transfer, but is preferably 10 nm or less, more preferably 5 nm or less.

[0101] In the photoelectric conversion element of the present invention, the hole transport layer 4 shown in FIG. 1 is a layer having a function of transporting holes, and is a layer located between the photoelectric conversion layer (perovskite layer) 3 and the counter electrode 5. The hole transport layer is used to improve the efficiency of hole transfer from the photoelectric conversion layer to the electrode and to block the transfer of electrons. For example, a conductor, a semiconductor, an organic hole transport material, etc. can be used for the hole transport layer, and an additive may be included for the purpose of further improving the hole transport properties.

[0102] The hole transport layer of the present invention is a layer containing, as a hole transport material, a compound represented by the general formula (1). In the hole transport layer of the present invention, two or more types of the compound represented by the general formula (1) may be used in combination, and the compound may also be used in combination with other hole transport materials not belonging to the present invention.

[0103] Specific examples of hole transport materials other than those of the hole transport material of the present invention include CuI and CuInSe. ２ Compound semiconductors containing monovalent copper such as CuS; GaP, NiO, CoO, FeO, Bi ２ O ３ , MoO ２ , Cr ２ O３ Examples of the organic hole transport material include compounds containing metals other than copper, such as copper oxides, and the like. These metal oxides may be mixed into the hole transport layer or may be laminated on the hole transport material. Examples of the organic hole transport material include polythiophene derivatives such as poly-3-hexylthiophene (P3HT) and polyethylenedioxythiophene (PEDOT), fluorene derivatives such as 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD), carbazole derivatives such as polyvinylcarbazole, triphenylamine derivatives such as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), diphenylamine derivatives, polysilane derivatives, and polyaniline derivatives.

[0104] As a method for forming the hole transport layer of the photoelectric conversion element of the present invention, any coating method for coating with a coating liquid can be used, and the same methods as those for forming the electron transport layer can be used.

[0105] In the present invention, the solvent used in the coating solution for the hole transport layer during film formation may be an aromatic organic solvent such as benzene, toluene, xylene, mesitylene, tetralin (1,2,3,4-tetrahydronaphthalene), monochlorobenzene (chlorobenzene), o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, or nitrobenzene; an alkyl halide organic solvent such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, or dichloromethane; a nitrile solvent such as benzonitrile or acetonitrile; or a tetrahydrofuran or dioxane. Examples of suitable solvents include, but are not limited to, ether solvents such as ethanol, diisopropyl ether, c-pentyl methyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate and propylene glycol monomethyl ether acetate; and alcohol solvents such as methanol, isopropanol, n-butanol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, cyclohexanol, and 2-n-butoxyethanol. Two or more of the above solvents may be mixed and used, and the solvent to be used can be selected depending on the structure. It is particularly preferable to use aromatic organic solvents and halogenated alkyl organic solvents.

[0106] In the present invention, the thickness of the hole transport layer is preferably from 5 to 500 nm, more preferably from 10 to 250 nm, from the viewpoint of further improving the photoelectric conversion efficiency.

[0107] In the present invention, the atmosphere during film formation of the hole transport layer is preferably a dry atmosphere, from the viewpoint of being able to reproducibly produce high-efficiency perovskite solar cells by preventing moisture from being mixed in. Furthermore, it is preferable to use a dehydrated solvent having a moisture content of 10 ppm or less.

[0108] In the present invention, the hole transport layer may contain a dopant (or an oxidizing agent) or a basic compound (or a basic additive) as an additive. Incorporating an additive into the hole transport layer to increase the carrier concentration of the hole transport material in the hole transport layer (doping) leads to an improvement in the photoelectric conversion efficiency of the photoelectric conversion element. In the present invention, when the hole transport layer contains a dopant and a basic additive as additives, the amount of the additive is preferably 4 equivalents or less per equivalent of the hole transport material.

[0109] In the present invention, when a dopant is contained, specific examples of the dopant include lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), silver bis(trifluoromethanesulfonyl)imide, zinc bis(trifluoromethanesulfonyl)imide (II), copper bis(trifluoromethanesulfonyl)imide (II), magnesium bis(trifluoromethanesulfonyl)imide (II), calcium bis(trifluoromethanesulfonyl)imide (II), tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III) tri[bis(trifluoromethane)sulfonimide] (FK209), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), tris(pentafluorophenyl)borane (BCF), and NOSbF. ６ , SbCl ５ , SbF ５ In the present invention, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is preferably used, but is not limited to this.

[0110] In the present invention, when a dopant is used, the amount is preferably 2.0 equivalents or less, more preferably 0.5 equivalents or less, relative to 1 equivalent of the hole transport material contained in the hole transport layer. While incorporating an additive into the hole transport layer improves the photoelectric conversion efficiency of the photoelectric conversion element, there are concerns that the use of a dopant additive may reduce the durability of a photoelectric conversion element using an organic compound and shorten the overall lifespan of the element (see, for example, Non-Patent Document 3). For this reason, there is a demand for the development of a photoelectric conversion element having a hole transport layer with a reduced dopant content. Furthermore, reducing the content would enable reductions in additive costs and manufacturing process costs.

[0111] In the present invention, a basic compound (basic additive) may be contained as an additive in the hole transport layer. When a basic compound is contained in the present invention, specific examples include 4-tert-butylpyridine (tBP), 2-picoline, and 2,6-lutidine. A basic compound is often used in combination with a dopant. In the present invention, it is also desirable to use a basic compound in combination with a dopant, and it is preferable to use 4-tert-butylpyridine.

[0112] In the present invention, when a basic compound is used, it is preferably used in an amount of 5 equivalents or less, more preferably 3.5 equivalents or less, per equivalent of the hole transport material of the present invention.

[0113] 1 is disposed opposite the conductive support 1 and formed on the hole transport layer 4, thereby enabling exchange of charges with the hole transport layer. In the photoelectric conversion element of the present invention, it is preferable to provide a metal electrode as a counter electrode on the hole transport layer 4, but it is also possible to add an electron blocking layer made of an organic material or an inorganic compound semiconductor between the hole transport layer 4 and the counter electrode 5.

[0114] In the present invention, specific examples of materials used for the counter electrode include metals such as platinum, titanium, stainless steel, aluminum, gold, silver, nickel, magnesium, chromium, cobalt, and copper, or alloys thereof. Among these, it is preferable to use gold, silver, or a silver alloy, as it exhibits high electrical conductivity even in a thin film. Examples of silver alloys include silver-gold alloys, silver-copper alloys, silver-palladium alloys, silver-copper-palladium alloys, and silver-platinum alloys, which are less susceptible to sulfidation or chlorination and improve the stability of the thin film.

[0115] In the present invention, the counter electrode is preferably made of a material that can be formed by a method such as vapor deposition.

[0116] When a metal electrode is used as the counter electrode, the thickness thereof is preferably 10 nm or more, more preferably 50 nm or more, in order to obtain good conductivity.

[0117] In the photoelectric conversion element of the present invention, the conductive support serves as the cathode, and the counter electrode serves as the anode. It is preferable to irradiate light such as sunlight from the conductive support side. When irradiated with sunlight, the photoelectric conversion layer (perovskite layer) absorbs the light and enters an excited state, generating electrons and holes. These electrons move through the electron transport layer, and the holes move through the hole transport layer to the electrode, causing a current to flow, and the element functions as a photoelectric conversion element.

[0118] When evaluating the performance (characteristics) of the photoelectric conversion element of the present invention, the short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency are measured. The short-circuit current density is the current flowing between the output terminals when the output terminals are short-circuited. ２ The open-circuit voltage is the voltage between the output terminals when they are open. The fill factor is the maximum output (product of current and voltage) divided by the product of the short-circuit current density and the open-circuit voltage, and is mainly affected by the internal resistance. The photoelectric conversion efficiency is the ratio of maximum output (W) to 1 cm ２ The initial photoelectric conversion efficiency is calculated by dividing the efficiency by the light intensity (W) per unit area and multiplying the result by 100. If the initial photoelectric conversion efficiency of the photoelectric conversion element having the element configuration of the present invention is 10% or more, it can be determined that the photoelectric conversion efficiency is good.

[0119] The photoelectric conversion element of the present invention can be applied to solar cells, various optical sensors, etc. The solar cell of the present invention is preferably a perovskite solar cell, and the perovskite solar cell can be obtained by arranging a required number of photoelectric conversion elements each containing a hole transport material containing the compound represented by general formula (1) as a hole transport layer, and arranging the required number of such cells to form a module and providing predetermined electrical wiring.

[0120] The hole transport material of the present invention can be applied not only to single-junction solar cells consisting of only perovskite solar cells, but also to multi-junction (tandem) solar cells, such as perovskite-perovskite and perovskite-silicon solar cells, but is not limited to these.

[0121] Although the preferred embodiment has been described above, the present invention is not limited to this, and may be modified as appropriate within the scope of the present invention.

[0122] The present invention will be specifically described below by way of examples with reference to the drawings, but the present invention is not limited to the following examples. １ This was measured using H-NMR (JNM-ECZ400S / L1 nuclear magnetic resonance spectrometer manufactured by JEOL Ltd.).

[0123] Synthesis Example 1 Synthesis of Compound (A-1) A reaction vessel was charged with the compound (0.20 g) of the following formula (10), the compound (0.46 g) of the following formula (11), tetrakis(triphenylphosphine)palladium(0) (0.030 g, manufactured by Tokyo Chemical Industry Co., Ltd.), potassium carbonate (0.41 g, manufactured by Kanto Chemical Co., Inc.), dimethylformamide (10 mL), and water (2.5 mL), and the mixture was degassed under reduced pressure. The mixture was stirred at 90°C for 7 hours under an argon atmosphere. After completion of the reaction, the mixture was poured into water (100 mL) and extracted with chloroform (200 mL). The separated organic layer was dehydrated over magnesium sulfate, and the filtrate obtained by filtration was concentrated under reduced pressure. The crude product was purified using a silica gel column (toluene:ethyl acetate = 100:0 to 25:1), and the purified fraction was concentrated under reduced pressure. The resulting solid was washed with methanol and dried under reduced pressure to obtain the compound of the following formula (A-1) as an orange solid. (Yield: 0.34 g, yield: 81%)

[0124] １ H-NMR (400MHz, DMSO-d ６ ): δ (ppm) = 8.98 (2H), 8.33 (2H), 7.64-7.70 (4H), 7.05-7.14 (8H), 6.90-6.97 (8H), 6.74-6.80 (4H), 3.73 (12H).

[0125]

[0126]

[0127] Synthesis Example 2 Synthesis of Compound (A-2) A reaction vessel was charged with the compound of formula (10) (0.16 g), the compound of formula (12) (0.76 g), tetrakis(triphenylphosphine)palladium(0) (0.025 g, manufactured by Tokyo Chemical Industry Co., Ltd.), potassium carbonate (0.41 g, manufactured by Kanto Chemical Co., Inc.), dimethylformamide (10 mL), and water (2.5 mL), followed by degassing under reduced pressure. The mixture was stirred at 90°C for 6 hours under an argon atmosphere. After completion of the reaction, the mixture was poured into water (150 mL) and extracted with chloroform (200 mL). The separated organic layer was dehydrated over magnesium sulfate, and the filtrate obtained by filtration was concentrated under reduced pressure. The crude product was purified using a silica gel column (toluene:ethyl acetate = 20:0 to 5:1), and the purified fraction was concentrated under reduced pressure. The resulting solid was washed with methanol and dried under reduced pressure to obtain the compound of formula (A-2) as an orange solid. (Yield: 0.29 g, yield: 44%)

[0128] １ H-NMR (400MHz, DMSO-d ６ ): δ (ppm) = 8.94 (2H), 8.36 (2H), 8.00 (4H), 7.54-7.56 (8H), 7.15-7.21 (4H), 6.99 (4H), 6.83 (16H), 6.66-6.71 (16H), 3.65 (24H).

[0129]

[0130] Synthesis Example 3 Synthesis of Compound (A-5) The compound of formula (10) (0.10 g), 4,4'-dimethoxydiphenylamine (0.12 g, manufactured by Tokyo Chemical Industry Co., Ltd.), sodium tert-butoxide (0.11 g, manufactured by Kanto Chemical Co., Inc.), and toluene (5 mL) were placed in a reaction vessel, and argon bubbling was performed for 15 minutes. Tri-tert-butylphosphine (0.046 g, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and palladium(II) acetate (0.009 g, manufactured by Tokyo Chemical Industry Co., Ltd.) were placed in the reaction solution, and the mixture was stirred at 110°C for 3 hours. After completion of the reaction, the mixture was filtered through Celite using toluene (50 mL), and the filtrate was concentrated under reduced pressure. The crude product was purified using a silica gel column (toluene:ethyl acetate=10:1), and the purified fraction was concentrated under reduced pressure and dried under reduced pressure to obtain the compound of the following formula (A-5) as an orange solid (yield: 0.032 g, 20%).

[0131] １ H-NMR (400MHz, CDCL ３ ): δ (ppm) = 8.72 (2H), 7.44 (2H), 7.21 (8H), 6.86 (8H), 3.81 (12H).

[0132]

[0133] Synthesis Example 4 Synthesis of Compound (A-51) A reaction vessel was charged with the compound of the following formula (13) (0.086 g), the compound of the above formula (12) (0.38 g), tetrakis(triphenylphosphine)palladium(0) (0.013 g, manufactured by Tokyo Chemical Industry Co., Ltd.), potassium carbonate (0.38 g, manufactured by Kanto Chemical Co., Inc.), dimethylformamide (5 mL), and water (1.4 mL), and the mixture was degassed under reduced pressure. The mixture was stirred at 90°C for 5.5 hours under an argon atmosphere. After completion of the reaction, the mixture was charged into water (50 mL) and extracted with toluene (100 mL). The separated organic layer was dehydrated over sodium sulfate, and the filtrate obtained by filtration was concentrated under reduced pressure. The crude product was purified using a silica gel column (toluene:ethyl acetate=10:1), and the purified fraction was concentrated under reduced pressure. The obtained solid was washed with methanol and dried under reduced pressure to obtain the compound of the following formula (A-51) as an orange solid. (Yield: 0.14 g, yield: 40%)

[0134] １H-NMR (400MHz, THF-d ８ ): δ (ppm) = 8.83 (1H), 8.65 (2H), 8.15 (4H), 7.75 (4H), 7.68 (4H), 7.37 (4H), 7.11 (4H), 6.93 (16H), 6.74 (16H), 3.70 (24H), 2.82 (3H).

[0135]

[0136] Synthesis Example 5 Synthesis of Compound (A-54) The compound of formula (10) (0.15 g), the compound of formula (14) (0.42 g), tetrakis(triphenylphosphine)palladium(0) (0.022 g, manufactured by Tokyo Chemical Industry Co., Ltd.), potassium carbonate (0.20 g, manufactured by Kanto Chemical Co., Inc.), dimethylformamide (6 mL), and water (1.5 mL) were placed in a reaction vessel and degassed under reduced pressure. The mixture was stirred at 80°C for 2 hours under an argon atmosphere. After completion of the reaction, the mixture was poured into water (50 mL) and extracted with toluene (100 mL). The separated organic layer was dehydrated over sodium sulfate, and the filtrate obtained by filtration was concentrated under reduced pressure. The crude product was purified using a silica gel column (toluene:ethyl acetate=20:1), and the purified fraction was concentrated under reduced pressure. The mixture was then re-purified using a silica gel column (NH silica gel, toluene:hexane=2:1), and the purified fraction was concentrated and dried under reduced pressure to obtain the compound of the following formula (A-54) as an orange solid (yield: 0.02 g, 5%).

[0137] １ H-NMR (400MHz, DMSO-d ６ ): δ (ppm) = 8.99 (2H), 8.36 (2H), 7.68 (2H), 7.53 (2H), 7.35-7.50 (6H), 7.22-7.35 (10H), 7.19 (4H), 7.09 (4H), 7.00 (8H), 4.82 (2H), 3.86 (2H), 1.99-2.17 (2H), 1.78-1.95 (4H), 1.53-1.75 (4H), 1.29-1.45 (2H).

[0138]

[0139] Example 1: Fabrication of a photoelectric conversion element and evaluation of current-voltage characteristics. A flat ITO-coated glass (conductive support 1, manufactured by Geomatec Co., Ltd.) was ultrasonically cleaned with isopropyl alcohol and then treated with UV ozone. In a dry atmosphere with a relative humidity of 10% or less, a coating solution for an electron transport layer, Tin(IV) oxide, 15% in H ２ Tin oxide colloidal dispersion (manufactured by Alfa Aesar) was spin-coated onto the ITO film, and then heated on a hot plate at 150° C. for 30 minutes to form a tin oxide layer (electron transport layer 2) with a thickness of about 20 nm.

[0140] In a dry atmosphere with a relative humidity of 10% or less, formamidine hydroiodide (1 M, manufactured by Tokyo Chemical Industry Co., Ltd.), lead(II) iodide (1.1 M, manufactured by Tokyo Chemical Industry Co., Ltd.), methylamine hydrobromide (0.2 M, manufactured by Tokyo Chemical Industry Co., Ltd.), and lead(II) bromide (0.2 M, manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in a mixed solvent of dimethylformamide and dimethyl sulfoxide in a volume ratio of 4:1. A dimethyl sulfoxide solution of cesium iodide (1.5 M, manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the solution so that the cesium content was 5% by composition ratio, thereby preparing a perovskite precursor solution. In a dry atmosphere with a relative humidity of 10% or less, the prepared perovskite precursor solution was dropped onto a tin oxide layer and spin-coated. 0.35 mL of chlorobenzene was added dropwise during spin-coating to form a perovskite precursor film. Then, by heating at 100°C for 1 hour using a hot plate, a Cs(MAFA)Pb(IBr) film with a film thickness of approximately 500 nm was obtained. ３ A layer (photoelectric conversion layer 3) was formed.

[0141] In a dry atmosphere with a relative humidity of 10% or less, lithium bis(trifluoromethanesulfonyl)imide as a dopant was dissolved in acetonitrile at a concentration of 1.8 M to prepare a dopant solution. Compound (A-1), the hole transport material obtained in Synthesis Example 1, was dissolved in chlorobenzene at room temperature at a concentration of 53 mM. 4-tert-butylpyridine was added thereto so that the amount was 3.3 equivalents relative to compound (A-1). Furthermore, the dopant solution was added so that the amount of lithium bis(trifluoromethanesulfonyl)imide was 0.5 equivalents relative to compound (A-1), to prepare a hole transport layer coating solution. In a dry atmosphere with a relative humidity of 10% or less, Cs(MAFA)Pb(IBr) ３ The hole transport layer coating solution was spin-coated onto the layer (photoelectric conversion layer 3) to form a hole transport layer 4 having a thickness of about 100 nm.

[0142] On the hole transport layer, a vacuum of 1×10 was applied by vacuum deposition. －４ A gold electrode (counter electrode 5) was formed by depositing a gold film of about 80 nm at about Pa, and a photoelectric conversion element was fabricated.

[0143] A simulated sunlight (AM 1.5, 1000 W / m) was generated using a white light irradiation device (Otento-Sun SH type, manufactured by Bunkoukeiki Co., Ltd.). ２ The photoelectric conversion element was irradiated with light from the conductive support side, and the current-voltage characteristics were measured using a source meter (Model 2400 Series Source Meter, manufactured by Keithley Corporation) to obtain the initial photoelectric conversion efficiency. The results are shown in Table 1.

[0144] [Example 2] A photoelectric conversion element was prepared in the same manner as in Example 1, except that compound (A-2) was dissolved at a concentration of 28 mM instead of compound (A-1), and the initial photoelectric conversion efficiency was obtained in the same manner as in Example 1. The results are shown in Table 1.

[0145] After obtaining the initial photoelectric conversion efficiency, the photoelectric conversion element was sealed in a zippered laminate bag (AL-8, Seisan Nippon Co., Ltd.) in a glove box under a nitrogen atmosphere. The sealed photoelectric conversion element was placed in a vacuum constant temperature dryer (VOS-310C, Tokyo Rikakikai Co., Ltd.) and stored at 85°C for 1,000 hours. The current-voltage characteristics were measured again under simulated solar light irradiation to obtain the photoelectric conversion efficiency after 1,000 hours of heating. The retention rate (%) calculated using the initial photoelectric conversion efficiency and the photoelectric conversion efficiency after 1,000 hours using the following formula (a-1) is shown in Table 2.

[0146]

[0147] Example 3 A photoelectric conversion element was prepared in the same manner as in Example 1, except that compound (A-5) was dissolved at a concentration of 42 mM at 60° C. instead of compound (A-1), and the initial photoelectric conversion efficiency was obtained in the same manner as in Example 1. The results are shown in Table 1.

[0148] Example 4 A photoelectric conversion element was prepared in the same manner as in Example 1, except that compound (A-51) was dissolved at a concentration of 65 mM at 60° C. instead of compound (A-1), and the initial photoelectric conversion efficiency was obtained in the same manner as in Example 1. The results are shown in Table 1.

[0149] After obtaining the initial photoelectric conversion efficiency, the photoelectric conversion efficiency after 1,000 hours of heating was obtained in the same manner as in Example 2. Table 2 shows the retention rate (%) calculated from the initial photoelectric conversion efficiency and the obtained photoelectric conversion efficiency after 1,000 hours of heating according to formula (a-1).

[0150] Example 5 A photoelectric conversion element was prepared in the same manner as in Example 1, except that compound (A-54) was dissolved at a concentration of 27 mM instead of compound (A-1), and the initial photoelectric conversion efficiency was obtained in the same manner as in Example 1. The results are shown in Table 1.

[0151] After obtaining the initial photoelectric conversion efficiency, the photoelectric conversion efficiency after 1,000 hours of heating was obtained in the same manner as in Example 2. Table 2 shows the retention rate (%) calculated from the initial photoelectric conversion efficiency and the obtained photoelectric conversion efficiency after 1,000 hours of heating according to formula (a-1).

[0152] Comparative Example 1 A photoelectric conversion element was prepared in the same manner as in Example 1, except that Spiro-OMeTAD (manufactured by Sigma-Aldrich), a standard hole transport material represented by the following formula (B-1), was dissolved in chlorobenzene at room temperature at a concentration of 70 mM and used instead of compound (A-1). The initial photoelectric conversion efficiency was obtained by measuring the current-voltage characteristics in the same manner as in Example 1. The results are shown in Table 1.

[0153] After obtaining the initial photoelectric conversion efficiency, the photoelectric conversion efficiency after 1,000 hours of heating was obtained in the same manner as in Example 2. The retention rates (%) calculated from the initial photoelectric conversion efficiency and the photoelectric conversion efficiency after 1,000 hours of heating according to formula (a-1) are shown in Table 2.

[0154]

[0155]

[0156]

[0157] The results in Table 1 show that the photoelectric conversion elements of the Examples, which used the compounds (A-1), (A-2), (A-5), (A-51) and (A-54) corresponding to general formula (1) as hole transport materials, exhibit superior photoelectric conversion efficiency compared to the photoelectric conversion element of Comparative Example 1, which used a standard hole transport material.

[0158] The results in Table 2 show that the photoelectric conversion elements of Example 2, which used the compounds (A-2), (A-51), and (A-54) corresponding to general formula (1) as hole transport materials, maintained high photoelectric conversion efficiency even after heating for 1000 hours, as compared with the photoelectric conversion element of Comparative Example 1, which used compound (B-1), a conventional standard hole transport material, and exhibited excellent heat resistance.

[0159] By using the compound having a dithienoquinoxaline skeleton of the present invention as a hole transport material, a photoelectric conversion element having good photoelectric conversion efficiency can be obtained. By using this photoelectric conversion element as a solar cell, solar energy can be efficiently converted into electrical energy, making it possible to provide clean energy.

[0160] REFERENCE SIGNS LIST 1 conductive support 2 electron transport layer 3 photoelectric conversion layer 4 hole transport layer 5 counter electrode

Claims

1. A compound represented by the following general formula (1): In the formula, R １ ~R ４ each independently represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms which may have a substituent, a linear or branched alkenyl group having 2 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 3 to 10 carbon atoms which may have a substituent, an aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent, or a heterocyclic group having 5 to 36 ring atoms which may have a substituent; R １ and R ２ , and R ３ and R ４ may be bonded to each other to form a ring. ５ and R ６ each independently represents a hydrogen atom, a halogen atom, a cyano group, a carboxyl group, a trimethylsilyl group, a linear or branched alkyl group having 1 to 20 carbon atoms which may have a substituent, a linear or branched alkenyl group having 2 to 20 carbon atoms which may have a substituent, a cycloalkyl group having 3 to 10 carbon atoms which may have a substituent, a linear or branched alkoxy group having 1 to 20 carbon atoms which may have a substituent, a cycloalkoxy group having 3 to 10 carbon atoms which may have a substituent, a linear or branched acyl group having 1 to 20 carbon atoms which may have a substituent, a thio group having 0 to 20 carbon atoms which may have a substituent, an amino group having 0 to 30 carbon atoms which may have a substituent, an aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent, or a heterocyclic group having 5 to 36 ring atoms which may have a substituent. １ and X ２ each independently represents a single bond, a divalent aromatic hydrocarbon group having 6 to 36 carbon atoms which may have a substituent, a divalent heterocyclic group having 5 to 36 ring atoms which may have a substituent, or a divalent group containing the aromatic hydrocarbon group and the heterocyclic group; X １ and R １ , X １ and R ２ , X ２ and R ３ , and X ２ and R ４ may be bonded to each other to form a ring.

2. In the general formula (1), R １ ~R ４ and each independently represent an unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a substituted aromatic hydrocarbon group having 6 to 36 carbon atoms.

3. In the general formula (1), X １ and X ２ are each independently a single bond or a divalent group of an unsubstituted aromatic hydrocarbon group having 6 to 36 carbon atoms.

4. A hole transport material comprising the compound according to any one of claims 1 to 3.

5. A photoelectric conversion element using the hole transport material according to claim 4.

6. A solar cell using the photoelectric conversion element according to claim 5.

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